Well I currently running an eclipse 8812 dvc woofer, rated at 500rms, giving it 600. Its in a box that is 30widex15tallx 13.25 deep, 35hz filled with poly. Would say upping my box size or changing the tuning (new box obviously) make the sub sound any better. I do get some tinsel slap at full tilt but with a sub that has 1.5in one way excursion its hard to avoid.
Size really isnt an issue since I am now in a station wagon, I just want to get the most out of the woofer without buying new stuff (I would LOVE to get 2-3 of these, but they are IMPOSSIBLE to locate anymore)